Evaluation of the inhibition effect of thiolated poly(acrylates) on vaginal membrane bound aminopeptidase N and release of the model drug LH-RH

The purpose of this study was to evaluate the inhibitory effect of thiolated carbopol 974P (carb-cys) on the enzymatic activity of vaginal aminopeptidase N in-vitro. Mediated by a carbodiimide, L-cysteine was covalently linked to carbopol 974P. Depending on the weight ratio of polymer to cysteine during the coupling reaction, resulting conjugates displayed 31.3-54.4 micromol thiol groups per g polymer. The inhibitory effect of carb-cys conjugates was evaluated towards isolated aminopeptidase N and aminopeptidase-N-like activity of excised vaginal mucosa covered with native mucus, respectively. Enzymatic activity was assayed spectrophotometrically using L-leucine-p-nitroanilide (L-leu-pNA) as a synthetic substrate. Carb-cys thereby showed a significantly higher inhibitory effect than unmodified polymer towards both isolated enzyme and vaginal mucosa. Moreover, enzyme inhibition was strongly dependent on the amount of thiol groups being immobilised. The more thiol groups available the higher was the inhibitory effect. Due to its additional high cohesive properties and the possibility of a sustained drug release, which could be shown for the model drug LH-RH, carb-cys appears interesting for the development of vaginal peptide drug-delivery systems.     

Estimation of the survival function for Gray's piecewise-constant time-varying coefficients model

Gray's extension of Cox's proportional hazards (PH) model for right-censored survival data allows for a departure from the PH assumption via introduction of time-varying regression coefficients (TVC). For this model estimation of the conditional hazard rate relies on the inclusion of penalized splines. Cubic penalized splines tend to be unstable in the right tail of the distribution and thus quadratic, linear and piecewise-constant penalized splines may be a favourable choice. We derive a survival function estimator for one important member of the class of TVC models--a piecewise-constant time-varying coefficients (PC-TVC) model. Using the first-order Taylor series approximation we also derive an estimate for the variance of the log-transformed and log(-log)-transformed survival function, which in turn leads to estimated confidence limits on the corresponding scales of the survival function. Accuracy in estimating underlying survival times and survival quantiles is assessed for both Cox's and Gray's PC-TVC model using a simulation study featuring scenarios violating the PH assumption. Finally, an example of the estimated survival functions and the corresponding confidence limits derived from Cox's PH and Gray's PC-TVC model, respectively, is presented for a liver transplant data set.     

Rheology and NMR self-diffusion experiments as well as skin permeation of diclofenac-sodium and cyproterone acetate of new gel preparations

The viscoelastic properties of two transparent semisolid preparations, one consisting of surfactant, paraffin oil, and water (BAS), and the other consisting of surfactant, cetylstearyl-2-ethylhexanoate, and water (CUBO), were characterized by oscillatory measurements. In (1)H-NMR diffusion experiments it was confirmed that the formulations are O/W systems, and the three-dimensional packing of the closed globular aggregates form a cubic structure. Moreover, standard diffusion experiments with porcine skin using Franz cells were performed with incorporated diclofenac-sodium and cyproterone acetate, respectively. The cumulative amount released after 48 h of diclofenac-sodium were excellent with 665.28 microg/cm(2) and with 36.7 microg/cm(2) for cyproterone acetate. The new drug-containing formulations were also prepared as transdermal patches by using carrageenan as a matrix. In diffusion studies zero-order kinetics was found for both drugs, but with a higher lag time for cyproterone acetate. The total work of adhesion was analyzed by tensile studies on porcine skin and found to be very good. The presented cubic gels as well as mixtures with carrageenan are promising alternative drug carrier systems for topical pharmaceutical as well as cosmetics.     

The use of mucoadhesive polymers in vaginal delivery

The vagina is an important area of the reproductive tract and serves as a potential route of drug administration. Beside locally acting drugs it is also of importance for systemic drug delivery, uterine targeting or even vaccination. Currently available dosage forms have several limitations, therefore novel concepts and dosage forms are needed. In this field mucoadhesive polymers will play a major role. After discussion of the anatomy and physiology of the vagina this review highlights the most important studies based on mucoadhesive polymer-systems like poly(acrylates), chitosan, cellulose derivatives, hyaluronic acid derivatives, pectin and traganth, starch, poly(ethylene glycol), sulfated polysaccharides, carrageenan, Na-alginate and gelatine.     

Anthranilic acid based CCK1 receptor antagonists: preliminary investigation on their second "touch point"

In this phase of structure-affinity relationship study of VL-0395, a new anthranilic acid based CCK1 selective antagonist, we propose a series of unnatural aminoacidic derivatives. The result of this work is the identification of a new CCK ligand, which possesses an affinity (IC50 = 35 nm) one order of magnitude greater than the lead and, as a general rule, it points out how the hypothesized receptorial pocket which accommodates the Phe residue allows much more structural modification than that interacting with the N-terminal group. Hence, the modification of the C-terminal pharmacophoric group of our lead VL-0395 can not only enhance the affinity of anthranilic acid derivatives but can modulate the selectivity for one CCK receptor subtype or afford mixed antagonists.     

Evaluation of the allergenic potential of Ginkgo biloba extracts

Ginkgo biloba extracts are used for the treatment of central and peripheral malperfusion, cerebral insufficiency and dementia. Between 1996 and 1998, several patients in Austria who had received parenteral Ginkgo extracts were reported to have developed allergy-like symptoms. The aim of the present study was to determine whether Ginkgo biloba extracts contain type I allergens. The protein content of Ginkgo biloba extracts was determined by BCA protein determination and SDS-PAGE. We used sera from 95 polysensitized plant-allergic patients (the sera contained IgE antibodies against most plant allergens), and rabbit antisera raised against defined recombinant plant allergens. The presence of allergens in Ginkgo extracts was determined by dot-blotting and Wester blot. Neither rabbit antisera nor IgE antibodies of patients reacted to the Ginkgo extracts. In addition, it was shown that prick testing of the skin could be conveniently used to study Gingko extracts for allergenic activity. In conclusion, no evidence for the presence of type I allergens in Ginkgo extracts was found. We recommend serological and/or skin testing to exclude sensitisation to components of Ginkgo biloba extracts.     

Thiolated Polymers: Development and Evaluation of Transdermal Delivery Systems for Progesterone

Purpose. To evaluate the possible use of polycarbophil-cysteine (PCP-Cys) as polymeric matrix for transdermal progesterone application. Methods. Thiolated polycarbophil was synthesised by the covalent attachment of cysteine to the basis polymer. The adhesive properties of PCP-Cys in comparison to polyvinylpyrrolidone/hydroxypropyl- methylcellulose (PVP/HPMC) and polyvinylpyrrolidone/polyvinyl- alcohol (PVP/PVA) were investigated by testing the total work of adhesion (TWA) on porcine skin. Release studies in Franz diffusion cells and standard in vitro permeation experiments with porcine skin were performed analysing the progesterone content by high-per- formance liquid chromatography.Results. Films based on PCP-Cys displayed very high cohesive properties due to the formation of interchain disulfide bonds. The TWA of the thiolated polymer on porcine skin was significantly (P <0.05) the highest. In addition progesterone permeation was also the highest from PCP-Cys compared with PVP/HPMC and PVP/PVA within 24 hours. Conclusion. PCP-Cys—a partly thiolated polymer—might be a novel polymer matrix for transdermal progesterone delivery with excellent adhesiveness on porcine skin.     

Development and in vitro evaluation of a mucoadhesive vaginal delivery system for progesterone.

The purpose of the present study was to design a novel carrier system based on a mucoadhesive polymer exhibiting improved properties concerning drug delivery to the vaginal mucosa. This was reached by the covalent attachment of L-cysteine to commercially available polyacrylic acid (Carbopol 974P). Mediated by a carbodiimide, increasing amounts of L-cysteine were covalently linked to the polymer. The resulting thiolated polyacrylic acid conjugates (NaC974P-Cys) displayed between 24.8 and 45.8 micromol thiol groups per gram of polymer. Because of the formation of intra- and/or intermolecular disulfide bonds, the viscosity of an aqueous thiolated polymer gel (3%) increased about 50% at pH 7.0 within 1 h. In oscillatory rheological measurements, it was shown that this increase in viscosity is mainly due to the increase in elasticity. Tensile studies carried out on freshly excised cow vagina demonstrated a significant (P<0.05) increase in the total work of adhesion (TWA) compared to the unmodified polymer. An amount of 24.8 micromol thiol groups per gram of polymer resulted in a 1.45-fold increase in the TWA, whereas an amount of 45.8 micromol showed an even 2.28-fold increase. These improved mucoadhesive properties can be explained by the formation of disulfide bonds between the thiolated polymer and cysteine rich subdomaines of the mucus layer. The release rate of the model drug progesterone from tablets based on microcrystalline cellulose serving as the reference was approximately 1% per hour, whereas it was 0.58% per hour for the unmodified polymer (NaC974P) and 0.12% per hour for the thiolated polymer (NaC974P-Cys). Therefore, this thiolated polymer is a promising carrier for progesterone providing a prolonged residence time and a controlled drug release.